Oxide TFT Floating Channel for High Mobility
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Solution Overview
Problem
Existing thin film transistors, such as amorphous silicon TFTs, face limitations in mobility and flexibility, while polycrystalline silicon TFTs suffer from manufacturing challenges and organic TFTs have lower mobility and higher leakage current, making them unsuitable for large, high-performance display devices.
Innovation Solution
The development of oxide thin film transistors with a floating channel structure, which includes a gate, gate insulating layer, channel, source, drain, and a floating channel formed from conductive materials, allowing for adjustable channel length and reduced resistance, enabling higher mobility and current efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFTs are used, then manufacturing cost is reduced and uniform formation on large substrates is achieved, but mobility is limited to about 0.5 cm²/Vs
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical properties while maintaining the low-cost manufacturing process. This material substitution enables mobility improvement to tens or hundreds of cm²/Vs without sacrificing the ease of manufacture on large substrates
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor channel layer with conventional silicon-based gate electrode and gate insulating layer. This composite approach leverages the high mobility advantage of oxide semiconductors while maintaining compatibility with existing silicon TFT manufacturing processes
2Speed
If polycrystalline silicon TFTs are used, then mobility increases to tens or hundreds of cm²/Vs, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the crystalline structure parameter from polycrystalline to amorphous oxide semiconductor, which simplifies the manufacturing process. The oxide semiconductor can be deposited as an amorphous film using low-temperature sputtering or ALD, eliminating the need for high-temperature crystallization processes required for poly-Si TFTs
Solution Approach 2:
The patent applies local quality by using oxide semiconductor specifically for the channel region where high mobility is critical, while other regions (gate electrode, source/drain) can use conventional materials. This targeted approach achieves high mobility where needed without requiring entire device fabrication to follow complex poly-Si processes
3Speed
If oxide semiconductor TFTs are used, then mobility increases and devices can be made larger, but electrical characteristics change due to damage or moisture adsorption
Solution Approach 1:
The patent implements beforehand cushioning by forming a protective layer (such as nitrogen-containing insulating layer or aluminum oxide) over the oxide semiconductor channel before device completion. This protective layer acts as a barrier against moisture and oxygen adsorption, preventing degradation of electrical characteristics while preserving the high mobility advantage
Solution Approach 2:
The patent creates an inert environment by enclosing the oxide semiconductor channel with protective layers that prevent contact with reactive species like moisture and oxygen. The nitrogen-containing insulating layer or aluminum oxide layer forms a protective atmosphere that stabilizes the electrical characteristics against environmental degradation
4Ease of manufacture
If organic TFTs are used, then manufacturing cost is reduced through wet process, but charge mobility decreases and leakage current increases
Solution Approach 1:
The patent changes the material type from organic semiconductor to inorganic oxide semiconductor, which fundamentally improves charge mobility from typically low values to tens or hundreds of cm²/Vs. This material substitution maintains compatibility with low-cost wet processing techniques while eliminating the mobility and leakage current disadvantages of organic TFTs
Data Source
Figure 1~2A
Figure 2B~2C
Figure 2D~2E
AI summary
A thin film transistor (TFT) and a method of manufacturing the same. The TFT may include a floating channel formed on a surface of a channel to be spaced apart from a source and a drain, and an insulating layer formed on the floating channel and designed to control a distance between the floating channel and the source or the drain.